1. Field of the Invention
The present invention relates to a vibrating mechanism which assures that a movable eccentric weight can simply be supported in a cylindrical casing thereof, and moreover, components constituting the vibrating mechanism can easily be assembled in the cylindrical casing. More particularly, the present invention relates to a mechanism for vibrating an amplitude variable type vibration compacting roller with the aid of the foregoing components. Further, the present invention relates to an apparatus for generating vibrations for a vibration compacting roller with a variable amplitude wherein the apparatus can properly control a quantity of eccentricity of the gravity center of a movable eccentric weight away from the center axis of a vibration generating shaft in the foregoing vibrating mechanism corresponding to given requirements. Moreover, the present invention relates to a method of generating vibrations for a vibration compacting roller with a variable amplitude by operation an apparatus of the foregoing type.
2. Description of the Related Art
Conventionally, a vibrating mechanism of the type for generating a certain intensity of vibration generating force by rotating a vibration generating shaft including a movable eccentric weight to utilize the centrifugal force induced by the eccentric weight has been often employed for a vibration utilizing machine such as a vibration utilizing type soil compacting roller, a vibration utilizing type pile driving machine or the like. When a certain given operation is performed using the vibrating mechanism, it is desirable that an amplitude of each vibration can be changed corresponding to given working conditions and so forth.
Here, it is assumed that a vibrating mechanism of the foregoing type is applied to a vibration compacting roller as a typical example of practical use thereof. To achieve a ground surface compacting operation at a high efficiency by operating the vibrating mechanism, it is desirable that an amplitude of each vibration is changed to another one depending on the kind of material to be compacted, a thickness of the compacted material and other conditions.
On the other hand, with respect to a conventional apparatus for generating variations for a vibration compacting roller with a variable amplitude (hereinafter referred to as a conventional vibration generating apparatus), many proposals have been hitherto made. Typically, the conventional vibration generating apparatus includes as essential components a vibration generating shaft disposed in a vibration rolling drum of the vibration compacting roller, a rotational driving unit for rotationally driving the vibration generating shaft in the normal/reverse direction, and a vibration generating force changing unit capable of changing a quantity of eccentricity of the gravity center of the eccentric weight away from the center axis of the vibration generating shaft. The fundamental structure of the conventional vibration generating apparatus is as shown in FIG. 11. Specifically, the conventional vibration generating apparatus includes a stationary eccentric weight 256 secured to a vibration generating shaft 255 and a pair of movable eccentric weight 257 and 257' each adapted to be turned relative to the stationary eccentric weight 256 so that the operative state represented by a low amplitude of each vibration is changed to the operative state represented by a high amplitude of each vibration, and vice versa depending on the direction of rotation of the vibration generating shaft 255, and moreover, an intensity of vibration generating force can be changed to another one by changing a quantity of eccentricity of the gravity center of each of the movable eccentric weights 257 and 257' away from the center axis of the vibration generating shaft 255 to another one. For example, when the vibration generating shaft 255 is rotated in the normal direction, the direction of deviation of the gravity center of each of the movable eccentric weights 257 and 257' away from the center axis of the vibration generating shaft 255 are reversely oriented in the opposite direction to the stationary eccentric weight 256 as represented by FIG. 11(a-1) and FIG. 11(a-2), whereby the vibration generating force is exerted on the vibration generating shaft 255 in such a direction that it is canceled, resulting in the vibration generating shaft 255 being rotated with a low amplitude of each vibration. On the contrary, when the vibration generating shaft 255 is rotated in the reverse direction, the direction of orientation of the stationary eccentric shaft 256 and the direction of deviation of the gravity center of each of the movable eccentric weights 257 and 257' away from the center axis of the vibration generating shaft 255 coincide with each other as represented by FIG. 11(b-1) and FIG. 11(b-2), resulting in the vibration generating shaft 255 being rotated with a high amplitude of each vibration because of the synthesization of both the vibration generating forces induced by the movable eccentric weights 257 and 257'.
The reason why a plurality of amplitudes, i.e., a high amplitude, a low amplitude and an intermediate amplitude of each vibration are required consists in a necessity for effectively performing a compacting operation by changing the applicable amplitude depending on a material to be compacted, a thickness of the material and so forth. For example, in the case that an asphalt based pavement material is compacted with a small thickness, each compacting operation is achieved with a low amplitude of each vibration in order to assure that gravel (crushed stone pieces) in the asphalt based pavement material is not broken or cracked, and moreover, surface flatness of the compacted material is not deteriorated due to the compaction operation achieved with a high magnitude of compacting force. On the other hand, when a soil based material supplied in the form of a belt having a large thickness is compacted like a compacting operation to be performed with a road bottom material, it is compacted with a high amplitude of each vibration in order to assure that a lower layer of the paved road can reliably be compacted with the vibration compacting roller.
When the vibrating rolling drum stopped under the condition in which said rolling drum is given vibration by rotating said vibration generating shaft 255, the compacted surface of the paved road brought in contact with said rolling drum is largely lowered. Thus it becomes difficult to finish the surface of the paved road smoothly. To prevent the foregoing malfunction from arising, a neutral position detecting limit switch is hitherto disposed on a frame having a forward/rearward movement lever mounted thereon in such a manner that the foregoing limit switch is actuated to the ON side when the forward/rearward movement lever is located at a forward movement position or at a rearward movement position, and it is actuated to the OFF side when the forward/rearward movement lever is located at a neutral position (stopped position).
FIG. 8 is a side view of a forward/rearward movement initiating unit 170, particularly showing the relationship between a forward/rearward movement lever 130 for the vibration compacting roller and a hydraulic pump operatively connected to each other to drivably running the vibration compacting roller. In response to a command issued to a vibration compacting roller driving system to instruct that the vibration compacting roller is caused to run with the aid of the forward/rearward movement initiating unit 170 by selectively displacing the forward/rearward movement lever 130 on an operator's seat to one of a forward movement position A, a neutral (stopped) position B and a rearward movement position C. The fundamental structure of the forward/rearward movement initiating unit 170 is such that an actuating arm 132 secured to a base shaft 131 is operatively associated with the forward/rearward movement lever 130, and a controlling lever 134 is operatively connected to the actuating arm 132 via a control cable 135 in order to change the direction of rotation of a variable capacity type hydraulic pump 133 to the opposite one for drivably running the vibration compacting roller, whereby a turning stroke of the actuating arm 132 is transmitted to the control lever 134. The variable capacity type hydraulic pump 133 is hydraulically connected to a vibration generating hydraulic motor (not shown) via a piping to vibratively drive the vibration rolling drum.
A cam 136 is formed integral with the base shaft 131, and a neutral position detecting limit switch 138 serving as forward/rearward movement lever neutral position detecting means is disposed on the frame 137 having the forward/rearward movement lever 130 mounted thereon. As the cam 135 is turnably displaced, the neutral position detecting limit switch 138 detects whether or not the forward/rearward movement lever 130 is located at one of the forward movement position A, the rearward movement position C and the neutral position B.
An amplitude changing switch 253 serving as vibration mode setting means is disposed in a signal circuit shown in FIG. 9 so as to actuate a solenoid driven change valve 252 shown in FIG. 10 that is a hydraulic circuit diagram. When the amplitude changing switch 253 shown in FIG. 9 is changeably actuated to the opposite side, the direction of supplying pressurized hydraulic oil from the hydraulic pump 251 to the hydraulic motor 250 shown in FIG. 10 is changed to the opposite direction, causing the direction of rotation of the hydraulic motor 250 to be changed from the normal direction to the reverse direction, and vice versa. The rotational driving force of the hydraulic motor 250 is transmitted to the vibration generating shaft 255 integrally connected to an output shaft of the hydraulic motor 250 in such a manner as to allow the vibration generating shaft 255 to be rotated in the same direction as that of the hydraulic motor 250. In FIG. 9, reference numeral 257 designates an automatic/manual changing switch.
When the running of the vibration compacting roller is stopped with the forward/rearward movement lever 130 shown in FIG. 8 displaced to the neutral position B as vibrations generated by the vibration generating shaft 255 are applied to the vibration rolling drum, the compacted ground surface having the vibration compacting roller brought in contact therewith in the vibration stopped state is largely lowered. Thus, it becomes difficult to smoothly finish the compacted road surface. To prevent the foregoing malfunction from arising, the neutral position detecting limit switch 138 serving as forward/rearward movement lever neutral position detecting means is hitherto actuated to the OFF side when the forward/rearward movement lever 130 is located at the position in the vicinity of the neutral position B between the forward movement position A and the rearward position C in order to enable the neutral position B of the forward/rearward movement lever 130 to be detected. Subsequently, the neutral position detecting limit switch 138 activates a vibration shaft rotation controlling unit 266. Specifically, a solenoid driven change valve 252 shown in FIG. 10 is restored to the original position thereof so that the supplying of pressurized hydraulic oil from the hydraulic pump 251 to the hydraulic motor 250 is interrupted with the result that the rotation of the vibration generating shaft 255 is stopped and the vibrative running of the vibration compacting roller is stopped. When the forward/rearward movement lever 130 is displaced to the forward movement A side or the rearward movement C side, the neutral position detecting limit switch 138 is actuated to the ON side again to activate the solenoid driven change valve 252, whereby pressurized hydraulic oil is supplied from the hydraulic pump 251 to the hydraulic motor 250, causing the vibration generating shaft 255 to be rotated so as to allow vibrations to be applied to the vibration compacting roller.
In the case of the conventional vibration compacting roller constructed in the above-described manner, when the forward/rearward movement lever 130 is displaced from the forward movement position A or the rearward movement position C to the neutral position B, the rotation of the vibration generating shaft 255 is stopped. However, the operative state of the vibration compacting roller coincides with a resonance point defined by the vibration rolling drum and the frame as well as another resonance point defined by the vibration rolling drum and the compacted ground surface in the course of shifting from the steady state having the vibration generating shaft 255 held in the rotating state to the immovable state having the vibration generating shaft 255 held in the vibration stopped state, resulting in the vibration rolling drum being caused to resonate. FIG. 12 is a graph which shows by way of example how the relationship among the number of revolutions of the vibration generating shaft, a magnitude of deviation of the gravity center of each of the movable eccentric weights 257 and 257' away from the center axis of the vibration generating shaft 255, and an intensity of decelerated vibration varies for a period of time from the state that the vibration generating shaft 255 is steadily rotated till the state that the rotation of the vibration generating shaft 255 is stopped, as time elapses. As is apparent from the graph, the number of revolutions of the vibration generating shaft 255 is gradually reduced from the point of time when the forward/rearward movement lever 130 is displaced to the neutral position, and in the shown case, the operative state of the vibration compacting roller coincides with a resonance point after a period of five seconds elapses. Obviously, at this time, the magnitude of deviation of the center axis of the vibration rolling drum away from that of the vibration compacting roller, i.e., an amplitude of each vibration is increased. Once the operative state of the vibration compacting roller coincides with the foregoing resonance point, a number of small corrugated ruggednesses are formed on the compacted ground surface having the vibration rolling drum brought in contact therewith.
On the contrary, when the forward/rearward movement lever 130 is displaced from the neutral position C to the forward movement position A or the rearward movement position B, the vibration rolling drum coincides with the resonance point in the course of shifting from the state that the number of revolution of the vibration generating shaft 255 is increased to that corresponding to the steady rotating state of the vibration generating shaft 255, resulting in the vibration rolling drum being likewise caused to resonate. Consequently, another drawback of the vibration rolling drum is such that a number of small corrugated ruggednesses are likewise formed on the compacted ground surface having the vibration rolling drum brought in contact therewith.
Usually, the vibration compacting roller reciprocably moves on the road surface within a predetermined working range several times to perform a rolling operation with the vibration rolling drum while the forward/rearward movement lever is changeably displaced with an operator's hand. Conventionally, however, since the rotation of the vibration generating shaft 255 is stopped every time the forward/rearward movement lever 130 is located at the neutral position (corresponding to the position where the rotation of the vibration rolling drum is stopped), it is necessary that starting and stopping of the rotation of the vibration generating shaft 255 are frequently conducted. This leads to the result that a large magnitude of load should be borne by the hydraulic pump and the vibration generating hydraulic motor every time the forward/rearward movement lever 130 is located at the neutral position, resulting in a large amount of energy loss arising. In addition, a large amount of time loss is caused not only when the vibration generating shaft 255 starts to be rotated but also when the rotation of the vibration generating shaft 255 is stopped.
With respect to a vibration compacting roller driving system wherein the direction of rotation of the vibration generating shaft 255 is changed to the opposite one to change an amplitude of each vibration to another one, there arises a problem that when the direction of rotation of the vibration generating shaft 255 in a certain direction is reversed while the rotation of the vibration generating shaft 255 is not still held in the vibration stopped state, the movable eccentric weights 257 and 257' are rotated further under the influence of inertia force induced in the foregoing state until they collide against an engagement portion of the stationary eccentric weight 256, resulting in components associated with the vibration generating shaft 255 being damaged or injured. In addition, since the direction of rotation of the vibration generating shaft 255 is reversed after it is once stopped when the direction of rotation of the vibration generating shaft 255 is changed to the opposite one, there arises another problem that a large amount of loss in a vibration rising time as well as a large amount of loss in a vibration stoppage time are caused, resulting in a large amount of energy being uselessly lost.
On the other hand, another example of a conventional variable amplitude type vibrating mechanism of the type adapted to change an amplitude of each vibration to another one without any changing of the direction of rotation of a vibration generating shaft to another one is disclosed in an official gazette of Japanese Patent Laid-Open Publication NO. 53-136773. This vibrating mechanism constructed according to the prior invention will be described below with reference to FIG. 13.
A cylindrical casing 51 includes cantilever-like shafts 56 and 57 on the opposite sides to serve as bearings. The cylindrical casing 51 is supported by end plates of a vibration rolling drum (not shown). A movable eccentric weight 52 is turnably disposed in the cylindrical casing 51 to turn around a pivotal shaft 53 which extends through the center axis of the cylindrical casing 51 at a right angle relative to the latter. With this construction, a magnitude of eccentric moment induced by the eccentric weight 52 can be changed to another one by dislocating the eccentric weight 52 around the pivotal shaft 52 in the cylindrical casing 51 so as to enable a quantity of vibrative movement transmitted from the eccentric weight 52 to the vibration rolling drum to be adjusted as desired.
According to the prior invention, the adjustment of the vibrative movement is achieved with the aid of an adjusting unit which is substantially composed of a plate 55 having a longitudinally extending slot 54 formed therethrough so as to enable the position of the slot 54 to be adjusted in the axial direction of the cylindrical casing 51. The right-hand end of the plate 55 is fixedly secured to an adjusting rod 58, while the left-handed end of the plate 55 is fixedly secured to an annular adjusting device 59. The pivotal shaft 53 for the eccentric weight 52 extends through the slot 54 of the plate 55, and the plate 55 can slidably be displaced in the longitudinal direction of the adjusting rod 58 without any hindrance caused due to the presence of the pivotal shaft 53. The eccentric weight 52 includes a driving rod 60 which extends through the slot 54 of the plate 55 in the transverse direction. As the plate 55 is axially displaced by the adjusting rod 58 in the leftward direction, the eccentric weight 52 is turnably displaced around the pivotal shaft 53 by the driving rod 60 while scribing a pivotal locus therewith, causing a magnitude of eccentric moment induced by the eccentric weight 52 to be changed as desired. Thus, an amplitude of vibrative movement induced by the eccentric weight 52 during rotation of the cylindrical casing 51 can be changed to another one corresponding to the deviation of the gravity center of the eccentric weight 52 from the center axis of the cylindrical casing 51.
Since the vibrating mechanism is constructed in the above-described manner, a hydraulic system and an eccentricity adjusting system for the vibrating mechanism can be designed with minimized dimensions, resulting in a danger of causing oil leakage from the hydraulic system being reduced or alleviated. In addition, an intensity of hydraulic pressure applied to the hydraulic system can reliably be set to a desired value.
In spite of the advantageous feature of the vibrating mechanism as mentioned above, the conventional vibrating mechanism has problems as noted below. Thus, many requests have been raised from users for solving these problems.
1. Since the cylindrical casing 51 is not designed to exhibit an opened structure, it is difficult to insert the eccentric weight 52 and associated components in the cylindrical casing 51 for assembling them together in the cylindrical casing 51. For this reason, it is not easy to perform an assembling operation with these components. PA0 2. While vibrations are successively generated by the vibrating mechanism, the cylindrical casing 51 is rotated at a high rotational speed, causing lubricant in the cylindrical casing 51 to forcibly adhere to the inner wall surface of the cylindrical casing 51 under the influence of the centrifugal force induced by the rotation of the cylindrical casing 51. This leads to the result that lubricant is less liable of reaching locations to be lubricated. Thus, it is difficult to properly lubricate the foregoing locations with the lubricant. PA0 3. As the adjusting rod 58 is displaced in the above-described manner, the driving rod 60 fitted to the eccentric weight 52 is followably displaced along a vertically extending slot 61 formed at a part of the slot 54, causing the adjusting rod 58 to be rotated about the center of turning movement of the eccentric weight 52. Thus, the driving rod 60 comes in slidable contact with the slot 61. As the adjusting rod 58 is repeatedly displaced in that way, the driving rod 60 increasingly wears, resulting in the driving rod 60 being rattled in the slot 61 due to the wearing of the driving rod 60. It is anticipated that it becomes difficult to properly locate the eccentric weight 52 in the cylindrical casing 51. PA0 4. Since the whole vibrating mechanism including the eccentric weight 52 and associated components is designed to exhibit such a closed structure that all the components are received in the cylindrical casing 51, a magnitude of inertia moment induced by the rotation of the cylindrical casing 51 is enlarged. Thus, a long time is required until the cylindrical casing 51 is rotated at a predetermined rotational speed, and moreover, a high intensity of energy is required to rotate the cylindrical casing 51 at a predetermined rotational speed. In addition, a long time is required until the rotation of the cylindrical casing 51 is stopped by reducing the rotational speed of the cylindrical casing 51 from the predetermined one.
Further, with respect to a conventional variable amplitude type vibration rolling drum adapted to change amplitude of each vibration to another one without changing the direction of rotation of the vibration generating shaft as shown in FIG. 13, there has been no disclosure in prior art as to how to control the amplitude of each vibration. This has been considered to be a problem preventing simple control operation of the vibration rolling drum in the practical operation.